Cooling air



1950 A. s. RICHARDSCN 2,525,045

COOLING AIR Filed March 5, 1946 2 Sheets-Sheet 1 COOLING OWR T E I l/IQMINE AIR SOLUTION FAN COOLER COOLER II u .ilku*-v/ INVENTOR ALLAN 5.RICHARDSON K) BY ATTORNEYS A. s. RICHARDSON Oct. 10,

- COOLING AIR Filed March 1946 2 Sheets-Sheet 2 INVENTO ALLAN S.RICHARDSON ,&MMA, Wadi M ATTORNEYS Patented Oct. 10, 1950 UNITED STATESPATENT OFFICE COOLING AIR Allan S. Richardson, Butte, Mont. ApplicationMarch 5, 1946, Serial No. 651,991 7 9 Claims. (01. 183-120) Thisinvention relates to cooling air by dehydration, and has for itsprincipal object the provision of an improved method and apparatus forthis purpose. This application is a continuationin-part of my priorcopending application Serial No. 527,125, now Patent No. 2,479,408,filed March 18, 1944.

In my above-mentioned application, I have described an improved methodof cooling warm humid mine air by absorption of the water vapor itcontains in a hygroscopic liquid, with accompanying transfer of heat toliquid. Heat from the liquid then is transferred to any suitable placeoutside the mine, and the liquid is regenerated by removal of absorbedwater therefrom. The present invention provides an improved coolingmethod particularly applicable for use in cooling mine air inconjunction with the foregoing method (although not limited to use inconjunction therewith); and further provides apparatus applicable foruse in carrying out the improved method.

It has heretofore been proposed (as, for example, in my aforementionedapplication) to absorb moisture from humid air by passing the air inintimate contact with a hygroscopic liquid. As an incidence to thisabsorption of the moisture, or water vapor, from the air, the heat ofcondensation of the water vapor is transferred to the liquid. This heatmay then be transferred through suitable heat exchange apparatus to apoint outside the mine or other space in which the air is being cooledor conditioned.

While the temperature of the air is not necessarily decreased by thisdehydration treatment, it feels substantially cooler, and it has asubstantially enhanced ability to cool moist surfaces, because inconsequence of its reduced moisture content a given volume of such aircan cause the evaporation of a larger quantity of moisture, and cause itto evaporate more rapidly, from the skin or other moist surface. Theheat of vaporization required for this evaporation is absorbed from themoisture itself and its immediate surroundings, with consequent coolingthereof.

The present invention contemplates an improved method, involvingabsorption of moisture from humid air in a hygroscopic agent, which notonly reduces the relative humidity of the air, but actually effects asubstantial lowering of its temperature, thus truly conditioning the air(as distinguished from simply cooling the air without reducing itsmoisture content or reducing its moisture content without substantiallylow ering its temperature). I

In accordance with the method of the invention, air at less thanrelative humidity is passed adiabatically in contact with liquid Waterat a temperature such that the relative humidity of the air is increasedand its temperature is decreased. The air is then dehydrated by passingit in contact with a hygroscopic agent. The hygroscopic agent is at atemperature somewhat above the wet-bulb temperature of the humidifiedair, but its vapor pressure is substantially below that of said air. Thetemperature and vapor pressure of the hygroscopic liquid are establishedat such values that, while the dry-bulb temperature of the air isincreased somewhat during dehydration, the moisture content of the airconcurrently is reduced to a value below that prior to humidification,and low enough to more than offset, in net cooling efiect, the increasein drybulb temperature. Thus the combination of humidification anddehydration steps results in a net cooling of the air, because duringhumidification the dry-bulb temperature of the air is reduced, andduring dehydration the relative humidity is reduced without permittingthe dry bulb temperature to rise to a value high enough to offset, inheating effect, the reduction in humidity. The heat of condensation ofthe moisture absorbed in the hygroscopic liquid is taken up largely inthe liquid. By repeating this sequence of steps a number of times, thedry-bulb temperature of the air may be very substantially reduced, andits relative humidity may be reduced to a comfortable value.

The hygroscopic liquid employed for dehydration is used at a temperaturesomewhat above the wet-bulb temperature of the air (advantageously at atemperature intermediate the dry-bulb temperature of the air before andafter humidification) because the liquid then will be at a temperature,after passage through the dehydration step, such that it may be cooledreadily by cooling water at about the wet-bulb temperature of the air..Since the hygroscopic liquid is heated during dehydration, and sinceits vapor pressure increases with increase in its temperature, coolingof the liquid is necessary. Cooling of the liquid is most convenientlyand economically carried out by use of cooling water cooled byevaporation into air. The temperature of cooling water thus cooledcannot be lower than the wet-bulb temperature of the air into whichevaporation 09- curs and in practice will actually be a few degreeswarmer than this temperature. By employing the hygroscopic liquid at atemperature above the wetbulb temperature of the air afterhumidification (when the dry-bulb and wet-bulb temperatures of the airare almost the same), the hygroscopic liquid is heated duringdehydration to a temperature high enough so that cooling water cooled byevaporation in the atmosphere may be used efficiently and economically.The fact that the dry-bulb temperature of the air is increased somewhatduring dehydration as a result of this procedure is not serious, and isbalanced by the economy resulting from efficient and economic cooling bywater which has been cooled by evaporation into the atmosphere.

Any appropriate hygroscopic agent may be used for dehydrating thehumidified air, but it is particularly advantageous to employ ahygroscopic liquid, such as an aqueous solution of calcium chloride,lithium chloride, zinc chloride, or ,diethylene glycol. The water-vaporpressure of the hygroscopic liquid (or other agent), with which the airis passed in contact after humidification, must, of course, have awater-vapor pressure less than that of the humidified'air.

For efiiciency in operation of the new method, it is advantageous toprevent any substantial entrainment of liquid water in the air passingfrom the humidification step to the dehydrating step, because suchentrained moisture is ineffective for cooling the air, and it willaccumulate in the dehydrating agent and will have to be removedtherefrom during regeneration.

The apparatus provided-by the invention comprises e, humidificationchamber, with-means for passing air into this chamber, and with meansfor introducing water therein and into contact with air passingtherethrough. Means are included for preventing entrainment of liquidwater in the humidified air. A dehydratin chamber is provided, togetherwith means for passing air from the humidification chamber into thedehydrating chamber, and means are arranged for introducing ahygroscopic liquid into a dehydrating chamber and into contact with airpassing therethrough.

In a, particularly advantageous embodiment of the invention, thereare-means for introducing air into the upper portion of thehumidification chamber and meansior'introducing liquid water also intothe upper portion of this chamber. Means are provided for directing thewater thus introduced downwardly in intimat concurrent contact with airpassing downwardly through this chamber. In this embodiment, a passageconnecting the lower portion of the humidification chamber and the lowerportion of the dehydrating chamber provides for conducting air from thehumidification chamber to the dehydrating chamber, and means areprovided for withdrawing air from the upper portion of the dehydratingchamber. Suitable-means'for introducing hygroscopic liquid into theupper portion of the dehydrating chamber also are provided, togetherwith means for directing the hygroscopic liquid downwardly in intimatecountercurrent contact with air passing upwardly through this chamber.

Advantageously the means for directing the water in the humidificationchamber and the hygroscopic liquid in the dehydrating chamber intointimate contact with the air comprise close- 1y spaced sinuous sheetsprovidingtortuous passages for the flow of 'air through the chambers.The means for introducing the water and the hygroscopic liquid thenpreferably are arranged to deliver the water. and the liquidrespectively to the upper portions of such sheets in the respectivechambers.

i The construction and ar-= rangernent of the sinuous sheets and themeans for delivering water or hygroscopic liquid to the surfaces thereofmay be as described in my Patent No. 2,231,088, dated February 11, 1941.

When sinuous sheets are employed within the humidification chamber, asis generally preferable, the means for preventing entrainment of liquidwater in the humidified air may be in the form of troughs arrangedadjacent the bottom of the sheets for collecting liquid water flowing tothe bottom thereof, and thus preventing its entrainment in air flowingbetween the sheets.

The invention is described more in detail below with particularreference to the accompanying drawings, showing an embodiment of theinvention as it may be arranged for cooling the air in mines, in whichFig. 1 is a schematic layout of the complete apparatus used for coolingmine air;

Fig. 2 shows a preferred arrangement of the apparatus comprising themine-air cooler and the connected solution cooler shown schematically inFig. 1;

Fig. 3 is a section taken substantially along the line AA of one of theair cooler units shown in Fig. 2; and

Fig. 4 is a section taken substantially along the line BB of Fig. 3.

The arrangement of apparatus shown schematically in Fig. l issubstantially as described in my above-mentioned application Serial No.527,125, now Patent No. 2,479,408. It comprises a cooling tower i havinga reservoir '2 for the accumulation of water and a pump 3 forcirculating the water from the reservoir through an air pre-coooler 4and up to the top of the tower through a pipe 5 to a distributor 5 fromwhich the water is sprayed into the tower and permitted to fall into thereservoir. Atmospheric air is blown by a fan I over the pro-cooler coilsand in countercurrent contact with the spray of water in the coolingtower, thereby cooling the water which enters the reservoir 2.

At a place inside the mine, preferably near the active working area, theapparatus H] for treating the mine air is installed. This apparatuscomprises a fan II for blowing the mine air to be treated into andthrough a mine-air cooler [2. The mine-air cooler includes means forfirst humidifying the air and then dehydrating it by bringing it intocontact with a hygroscopic solution. A solution cooler l3,advantageously located near the mine-air cooler 12, is provided formaintaining the temperature of the hygroscopic solution within properlimits. The hygroscopic solution from the mine-air cooler circulatesthrough a pipe 14 through the solution cooler, and is returned by a pumpl5 through piping i6 to the mine-air cooler. In the solution cooler I3,the liquid circulates in heat exchange contact with cooled water broughtfrom the reservoir 2 through piping IT and returned to the top of thecooling tower l by means of a pump [8 and piping [9. It is apparent thatliquid in the piping it and I9 is substantially in hydrostatic balance,and the pump 18 therefore serves mainly to over come the frictionalresistance in the piping to effect circulation.

A part of the hygroscopic solution circulating through the solutioncooler I5 is continuously removed and sent through piping 2G to asuitable regenerator for concentration, such as an evaporator, or arefrigerating unit whereinthe water is removed by freezing. Regeneratedsolution is,

of "coursepreturned to the apparatus through piping 2|.

Liquid Water for humidifying the air prior to dehydrating it by contactwith the hygroscopic liquid is circulated through the ,mine-air cooler[0,. through suitable piping 22 and 23.

The mine-air cooler assembly of chambers and the associatedsolution-cooler apparatus is shown more in detail in Figs. 2 to 4. Thefan il takes air from the mine or other space to be cooled and blows itthrough a duct 25 into and through a series of air-cooler units, each.comprising a humidification chamber 26 and a dehydrating chamber 21.Cooled and dehydrated air from the last dehydrating chamber in theseriespasses through a duct 28 back into the spacerin which the cooled air isdesired.

Each of the humidifying chambers 26 is in the form of a tower, in whichare mounted a considerable number of closely spaced, vertically arrangedsinuous sheets 30 (Figs; 3 and 4) These sheets provide tortuous passages3| for the flow of gas between them and advantageously are of the formdescribed in my above-mentioned Patent No. 2,231,088.

In order to humidify the air as it flows through each of thehumidification chambers 26, water from a supply tank 32 is pumped intoeach of these chambers by a pump 33 through the piping 22. The piping 22feeds a header 34 to which a number of spray pipes 35 and 33 areconnected. These spray pipes enter the humidification chamber 26 anddistribute the water in the form of a film on each side of the sinuoussheets 3!). The water flows down the sheets in concurrent rela tion withthe air flowing between the sheets, and water reaching the bottom of thesheets drains into troughs 37, disposed adjacent the bottoms of thesheets. Water collected in the troughs 3T drains into a header 38 towhich the piping 23 is connected for the purpose of returning thesurplus water to the storage tank 32.

As the air flows downwardly through the tortuous passages 3| between thesheets 30, its direction of flow is continually being reversed, and itis brought into intimate concurrent contact with the film of waterflowing downwardly from the spray pipes 35 and 36 along both sides ofthe sheets 30. This intimate contact favors evaporation of the waterinto the air flowing between the sheets. Conditions within the chambersare substantially adiabatic (that is, no heat is supplied from anexternal source to the air-water system within the chamber and none isabstracted therefrom to a point external of the system). Consequently,the heat of vaporization required for evaporating the water from thesheets into the air must come from within. the system itself. Some ofthe heat may be supplied by the water flowing down the sheets, and if soit will be correspondingly cooled, but a large portion is supplied bythe air into whichthe water evaporates, and the dry-bulb temperature ofthe air is, therefore, reduced as it flows down between the sheets andasits relative humidity is increased. Advantageously the air is humidifiedas closely as possible to saturation (100% relative humidity), for thenmaximum reduction in the dry-bulb temperature of the air is effected,subsequent dehydrating is facilitated, and a'minimum number ofsuccessive humidification .and dehydrating steps is necessary to efiecta given total degree of cooling.

:Water lost in the humidification chamber by evaporation into the airmay be replenished by supplying fresh water through piping 40 and (iffrom a source (not shown) to the storage tanks 32. Since watercirculated in closed circuit through each humidification chamber assumesthe wet-bulb temperature of the air passing through that chamber, bestresults are obtained by using a separate water storage tank inconnection with each humidification chamber in the series, as shown inthe drawings, but it is possible to supply the several humidiflcationchambers from a common storage tank.

Humidified air from the humidification chamber 26 flows through-apassage 42 connecting the lower portion of the humidification chamber 26with the lower portion of the associated dehydration chamber 21, andflows upwardly through the latter chamber. The dehydrating chamber isconstructed similarly to the humidification chamber, and has suspendedwithin it aconsiderable number of closely spaced, substantially verticalsinuous plates, arranged in the same manner as described above inconnection with the humidification chamber. As in the latter chamber,these plates define a series of tortuous passages through which the airflows upwardly in its passage through the dehydrating chamber.

Each of the dehydrating chambers is supplied with a hygroscopic solutionfed to it by the pumps I5 through piping E6. The pipes l6 connect withheaders 43, one of which is associated with each dehydrating chamber. Anumber of spray pipes are connected to each header and deliverhygroscopic liquid to both surfaces of the sinuous sheets within therespective dehydrating chambers in the same manner as water is deliveredto th corresponding sheets in the humidification chamber. Thehygroscopic liquid flowing along the surfaces and to the bottom of thesheets is collected in troughs and drains into a collecting header atthebottom of the dehydrating chamber, again in the same fashion asdescribed above with reference to the humidification chamber. Thecollected liquid is returned through the piping It to the particularcooling unit 44, 45, 46 or 41 from r which the solution was originallyfed by the pump [5 to the dehydrating chamber.

As humid, cooled air from the humidification chamber flows upwardlythrough the tortuous passages in the dehydrating chambers, the air isbrought into intimate countercurrent contact with the downwardly flowingfilm of hygroscopic solution on the sinuous plates within this chamber.The hygroscopic liquid (which may be an aqueous solution of calcium,zinc, or lithium chloride, or of diethylene glycol) is supplied to thedehydration chamber at a temperature somewhat above the wet-bulbtemperature of the humidified air (say at a temperature intermediate itsdry-bulb temperature prior to humidification and its wet-bulbtemperature after humidification) and at a concentration such that itswatervapor pressure is less than the water-vapor pressure of the airpassing in contact therewith. In consequence, moisture is absorbed fromthe air into the solution and the relative humidity of the air thus isdecreased Absorption of the water vapor in the hygroscopic liquid may beconsidered equivalent to condensation of the vapor, and in any eventresults in liberation of heat equivalent to the heat of vaporization ofthe amount of moisture thus absorbed. For the most part the liberatedheat is transferred directly to the hygroscopic liquid in which thewater vapor'is absorbed, so that the temperature of the liquid isincreased appreciably. The drybulb temperature of the air also isincreased during this step, by heat exchange. with the hygroscopicliquid, but this increased temperature of th air (at least in the secondandgsubsequent dehydration chambers) still is lower than its drybulbtemperature prior to humidification, and with the reduction in itsrelative humidity which dehydration brings about, the net result is toefiect a substantial cooling of the air.

Since the hygroscopic liquid is appreciably warmed during dehydration ofthe air, and since the vapor pressure of the hygroscopic liquid ismarkedly increased by an increase in its temperature, it is necessaryfor most eificient and economical operations to cool the liquidwithdrawn from the bottom of the dehydration chamber before returning itfor reuse. This cooling is accomplished in the cooling units 44, 45, 46and 41, forming components of the solution cooler l3 diagrammaticallyrepresented in Fig. 1. As shown in Fig. 2, a separate cooling unit isassociated with each dehydrating chamber in the series. Th warmedhygroscopic solution flowing from each of the dehydrating chambers tothe associated cooling unit is sprayed by a head 48 over and in heatexchange relation with cooling coils 50 within each unit. The coolingcoils in the several cooling units are connected in series,

and cooled water flows to them through the piping I! from the coolingtower I (Fig. 1), and is returned from them to the cooling tower throughthe piping l9. As the hygroscopic liquid is used at a temperature abovethe wet-bulb temperature of the humidified air, and as its temperatureis still further increased during dehydration, it is warm enough whenwithdrawn from the dehydration chamber so that it can be adequately andeconomically cooled by .water from the cooling tower I.

As shown in Fig. 2, the fiow of cooling water through the severalcooling units 44, 45, 46 and 41 is countercurrent to the flow of airthrough the associated dehydrating chambers. As more fully described inmy above-mentioned application Serial No. 527,125, this arrangementprovides that the hygroscopic solution fed to the last dehydratingchamber in the series is most effectively cooled and thus has the lowestvapor pressure, so that air discharged from the last dehydrating chamberwill have its moisture content (relative humidity) reduced to thegreatest practical extent.

Hygroscopic liquid flowing through the several dehydrating chambers, inaddition to being warmed by the absorption of moisture from the air, isalso diluted somewhat by the absorbed moisture. Since the water-vaporpressure of the hygroscopic solution is in part dependent upon itsconcentration (in general being increased by a decrease inconcentration), provision is made for continuously withdrawing a portionof the hygroscopic liquid from the system, regenerating it by theremoval of water, and returning the regenerated solution to the system.In the embodiment here particularly described, this is accomplished byproviding for the flow 'of hygroscopic liquid from the cooling unit 44associated with the first dehydrating unit in the series, through a pipe5! into the next cooling unit 45 in the series, and also for the flow ofhygroscopic liquid from the last cooling unit 41 in the series throughpiping 52 into the same cooling unit 45. Hygroscopic liquid from thesecond cooling unit 45 flows through a pipe 53 into the third coolingunit 46. Surplus hygroscopic liquid accumulatin'g in this latter coolingunit 46 flows through the pipe 20 to the regeneration means (not shown)where the liquid is concentrated by the removal of water (as byevaporation or freezing), and the concentrated liquid is returnedthrough piping 2] to both the first and the last cooling units 44 and 41in the series.

Hydrometer-actuated control valves 54 and 55 in the piping system 2| maybe provided-to regulate the admission of regenerated liquid to each ofthe first and last cooling units 44 and 41 in accordance with the extentto which the liquid in these cooling units is diluted, and so requiresreplenishment with fresh concentrated solution.

As described in my above-mentioned application Serial No. 527,125 nowPatent No. 2,479,408, this arrangement for circulating the hygroscopicliquid between the several separate cooling units, for withdrawingliquid for regeneration from an intermediate unit, and for returningregenerated liquid to the first and last units insures most efficientand economic operation of the system as a whole. This results from thefollowing several circumstances:

(1) The air flowing through the first dehydrating chamber in the seriesis at a higher wetbulb temperature than in any later dehydratingchamber, and so can best be dehydrated by bringing it in contact withfresh hygroscopic liquid. Further, the cooling unit 44 associated withthe first dehydrating chamber is the last in the series from thestandpoint of the flow of cooling water, and so is least effectivelycooled. By supplying hygroscopic liquid at maximum concentration to thiscooling unit and from it to the first dehydrating chamber in the series,the liquid can absorb more moisture from the air and hence be heated toa higher temperature than would be possible if solution at a more diluteconcentration were here supplied. Consequently, such concentrated liquidcan be better cooled by the cooling water which has already flowedthrough all other cooling units in the series and is at its highesttemperature prior to return to the cooling tower.

(2) Since air from the last dehydrating chamber in the series is to bedischarged into the working space in the mine, or other space wherecooled and dehydrated air is desired, it is advisable, for purposes ofmaximum dehydration, to insure that in passing through the lastdehydrating chamber the air comes in contact with hygroscopic liquidfrom the coolest and most concentrated body thereof. This is insured, inthe arrangement shown, by the provision for introducing freshconcentrated liquid to the cooling unit 41 and by providing that thiscooling unit is the first into which the cooling water flows from thecooling tower.

(3) The intermediate cooling units serve to maintain the hygroscopicliquid circulating through the intermediate dehydrating chambers incondition for effecting maximum economical dehydration of the airpreparatory to the next successive humidification and cooling step.I-Iygroscopic liquid accumulating in the cooling unit 46 associated withthe next to the last in the series of dehydrating chambers is at itsmost dilute concentration. By withdrawing hygroscopic liquid from thisbody for regeneration purposes, the liquid can be most economicallyconcentrated, and with minimum circulation through the concentratingapparatus.

Provision according to the invention for the use of hygroscopic liquidthat is at a temperature progressively higher in each successive dehydration stage proceeding in-adirection countercurrently to the direction ofair flow and concurrently to the, direction of cooling water flow,results in total Jheating of the hygroscopic liquid through awidetemperature range and to ahigh final temperature. .Inconsequence,cooling of the liquid is very efficiently efiectedby evaporationcooledwater. Iniact the temperature range through which the cooling water isheated'may range from a number of degrees below the atmospheric wet-bulbtemperature to forty or more degrees above this temperature. It isevident that this permits efiicient and economic transfer of heat fromthe air being cooled to the place where it is dissipated. At the sametime provision for first humidifying and then dehydrating the air, andpreferably repeating these steps a number of times, results insubstantial cooling of the air. Hence the invention is particularlyadvantageous for use where it is desirednot only to reduce the humidityof the air (thus increasing its ability to cool moist surfaces), butwhere it is also desired actually to reduce the temperature of the air.vBy passing the air repeatedly through the series of towers in which theair is first humidified and then dehydrated, the ultimate decrease inwet-bulb temperature will amount substantially to the sum of the severalseparate wet-bulb temperature reductions. At the same time, if theincoming air is particularly humid, the method and apparatus of theinvention are eifective for reducing the humidity to a comfortablevalue.

I claim:

1. The method of cooling air which comprises passing the air at lessthan 100% relative humidity adiabatically in contact with liquid waterat a temperature such that the relative humidity of the air is increasedand its dry-bulb temperature is appreciabl decreased, and thendehydrating said air by passing it in contact with a hygroscopic liquidhaving a temperature substantially above the dry-bulb temperature of thehumidified air but having a vapor pressure substantially below that ofsaid air, the temperature and vapor pressure of said liquid being suchthat the drybulb temperature of the air after dehydrating is increasedand the moisture content of said air is reduced to a value below thatprior to humidification and low enough to more than ofiset in coolingeffect the increase in dry-bulb temperature, the temperature of saidhygroscopic liquid being increased during dehydration sufficiently so asto permit efiective cooling thereof by water at about the wet-bulbtemperature of the atmospheric air.

2. The method of cooling air which comprises repeatedly subjecting theair to the sequence of steps comprising adiabatically humidifying theair to a high relative humidity, whereby its drybulb temperature issubstantially decreased, and then dehydrating the air by passing it incontact with a hygroscopic agent having a temperature substantiallyabove the dry-bulb temperatures of the air after humidification andhaving a vapor pressure substantially below that of the air introducedin contact therewith, whereby the wetbulb temperature of the air isdecreased to a value below the corresponding values prior tohumidification, and whereby the hygroscopic liquid is heated to a valuesufficientlyhigh to permit effective cooling thereof by water at atemperature near the wet-bulb temperature of the atmospheric air.

10 3. The method of cooling air which comprises adiabaticallyhumidifying the air, whereby its dry-bulb temperature is decreased andits relative humidit is increased, then passing the air thro gh adehydrating chamberin contact with ahygroscopic liquid having atemperature which is intermediate the drybulb temperatures of the airbefore and after humidification but which is substantially above thedry-bulb temperature of the air after humidification, and having a vaporpressure substantially below that of the humidified air, whereby the airis dehydrated and its dry bulb temperature is increased butinsuificiently to offset in cooling effect the effect of saiddehydration, and whereb the temperature of the hygroscopic liquid issubstantially increased, withdrawing the heated hygroscopic liquid fromsaid chamber and cooling it to a temperature above the dry-bulbtemperature of the humidified air by passing it in heat exchangerelation with cooling water cooled by evaporation in air, andreintroducing the cooled hygroscopic solution into said chamber.

4. The method of cooling air which comprises humidifying the air bypassing it downwardly through a chamber in concurrent contact withliquid water, recirculating the water through said chamber, thencepassing the air upwardly through a second chamber in countercurrentcontact with a hygroscopic liquid having a temperature substantiallyabove the dry-bulb temperature of the humidified air but having awatervapor pressure less than that of the air in contact therewith,whereby said hygroscopic liquid is heated to a still higher temperature,withdrawing said liquid from adjacent the bottom of said chamber,cooling said liquid to a temperature above the dry-bulb temperature ofthe humidified air, and introducing the cooled liquid at saidtemperature into said second chamber adjacent the top thereof.

5. The method of cooling air which comprises passing the air throughtortuous air passages in contact with films of liquid water, maintainingsubstantially adiabatic conditions within said passages, whereby therelative humidity of the air is increased and its dry-bulb temperatureis decreased, and passing the cooled and humidified air substantiallyfree of entrained liquid Water through tortuous passages in contact withfilms of a hygroscopic liquid having a temperature substantially abovethe dry-bulb temperature of the humidified air but having a watervaporpressure less than that of the humidified air, whereby the dry-bulbtemperature of the air is increased but its wet-bulb temperature isdecreased sufiiciently to more than ofiset in cooling effect saidincrease in dry-bulb temperature increase.

6. The method of cooling air which comprises humidifying said air underadiabatic conditions by passing it in contact with liquid water, thencepassing the air in contact with several separate bodies of hygroscopicsolution, flowing liquid from the first and last bodies to at least oneintermediate relatively dilute body, withdrawing and regeneratingsolution from said intermediate body by removing water therefrom, andreintroducing the regenerated solution into said first and last bodies.

7. The method of cooling air which comprises passing the air through aseries of several chambers in each of which the air first is passedthrough a humidification section under adiabatic conditions in contactwith liquid water, whereby the relative humidity of theair is'increased,and then is passed through a dehydrating section in contact with ahygroscopic solution having a water-vapor pressure less than that of theair in contact therewith, whereby the relative h midity of the air isdecreased and the temperature of the solution is increased and itsconcentration decreased, circulating solution from each of saiddehydrating sections through a separate cooling vessel associatedtherewith and thence back to the dehydrating section, flowing solutionfrom the first and last of said cooling vessels to at least oneintermediate vessel, withdrawing solution from said intermediate vesseland regenerating it by removal of water therefrom, and returning theregeneratedsolution. to the first and last of said, vessels.

8. Apparatus for cooling air comprising a humidification chamber, meansfor introducing air into the upper portion of said chamber, means forintroducing liquid water into the upperportion of said chamber, meansfor directing the water downwardly in intimate concurrent contact withair passing downwardly through said chamber, a

dehydrating chamber, a passage-connecting the lower portions'of bothchambers for conducting air from the humidification chamber to thedehydrating chamber, means for withdrawing air from the upper portionofsaid dehydrating-chamber, means for introducing a hygroscopic liquidinto :the;upper portion of said dehydrating chamber, and means fordirecting the hygroscopic liquid downwardly in, intimate countercurrent12 contact: with air 'passing upwardly through said, dehydratingchamber.

95 Apparatus for cooling'air: comprising a' humidification chamber sideby'side with a dehydrating chamber, said chambers being in communicationat their'lower ends, means'for delivering.

air into the upper end of'the-humidification chamber and for withdrawingair fromthe upper end of the dehydrating'chamber, closely spaced. sinuous sheets in each of. said chambers providing tortuouspassagesfor-the'flow of air therethrough, means for deliveringliquid'water to the upper portions of the sheets. in the humidificationchamber, and means for delivering ahygroscopic liquid to the upperportion of the sheets in the dehydrating chamber.

ALLAN S; RICHARDSON.

REFERENCES. CITED The following references are of record in the file ofthis patent:

UNITED. STATES'RA'IENTS Number Name Date 386,777 Griesser' .July 24',1888 2,062,771 Stead .Dec. 1, 1936 2,090,287 Corneliusi= Aug. 17, 19372,090,466 Bi'chowsky Aug; 17, 1937 2,231,088 Richardson- Feb. 11', 19412,479,408 Richardson Aug. 16, 1949 FOREIGN PATENTS Number Country, Date346,005 Germany May 15, 1919

